Annealing case necks

How do you when it is time to anneal the necks? I am shooting a 308 and 300 RUM and have noticed that the amount of effort that it takes to resize them using a Redding bushing die varies from case to case. I have checked for uniform neck thickness, which they are. I've also tried using the same amount of case lube on the neck.

You may go 5 or even 7 shots on the 308, depending how hot. I like 4. The Rum, 3 to
4, some guys do 1 or 2 firings on big mag brass. There is a guy on the hide "killshot"
that decaps, tumbles in stainless media and anneals for .10 cents a case. 72 hour turn
around.
Your resizing pressure won't be affecting by annealing. At least it better not be.

I usually anneal every other firing on my .308 Win. For one reason only and it is not for the resizing force that it takes. I noticed a couple years ago that when I started to seat the bullets I would have differences in the force it took to seat the bullet my groups would start to open up. I was annealing every 5th reloading at that time. I began watching this and doing the annealing more often and noticed that after the second firing I would see differences by the third loading so I finally just settled on every other time. Groups stayed tight after that. My brass is exclusively L.C. brass and I have way more loadings on my casings than I ever did when I was doing the 5th load annealing. Some might disagree with this but its just what I found with my rifle. I have noticed that some rifles don't need it near as often but I think the necks might be tighter on those guns. Mine is a factory Rem 700 VSF and probably has a bit looser chamber than a custom job does and works the brass a bit more.

I anneal every time I reload. It's probably overkill but now I don't have to keep track of how many times a case has been fired. I also figure it's the best way to make sure neck tension is consistent. It's simple, quick and inexpensive so why not?

For my 7WSM, 338LM, 338LM Improved I anneal every other firinging. They show very consistent neck tension.

How do you measure neck tension?

Took a new Federal .308 Win. case, loaded it with a Fed 210 primer, 42 grains of IMR4895 and seated a Sierra 165 SPBT bullet in it. Fired it. Deprimed it, cleaned its outside then lightly lubed it. Full length sized it with a gelded die whose neck was 3 thousandths smaller than the loaded round and setting the fired case shoulder back 2 to 3 thousandths. Reloaded that same case with the same components then fired it again and again and again....46 more times before running out of test powder.

Muzzle velocity spread was 33 fps, standard deviation was 10.

Had to trim it back every 10 reloads as it grew up to my 2.10" limit.

Didn't think any annealing was needed.

Friend of mine did a similar test but ran out of powder at 58 rounds. He didn't anneal his case either.

I've used the same type of full length sizing die on 30 caliber magnums getting 14 reloads per case without annealing.

I guess the reason is the case necks didn't change diameters much when sized down; no expander ball was used to work the case neck about twice as much as it would.

I don't do it often either(don't size much, turned necks, small clearances).
I cannot measure actual tension (right now). But I do measure pre-seating force with a loadcell built into an expander die. With a Wilson ND I can adjust necks to match seating force in each.
When this get's at all labor intensive, it's time to stress relieve necks.
Let the evil out..

A real downside I can think of in 'annealing' is that it is not what is desired, yet it's very easy to do. What is desired is deep stress relieving, which is a lower temp than annealing.
I use a lead dip, and if I used a flame system it would be a machine(for consistency and convenience).
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